Every now and then a story comes along that seems to be true in spite of every cell in your brain telling you it can't be. Welcome to one of those stories.In 2006, you'll remember that the International Astronomical Union announced that Pluto was to be expelled from the planetary club, reducing the number of planets in the solar system to eight. Cue mayhem in schools, where teachers were obliged to rip up wallcharts and console their pupils, who were understandably forlorn at the fate of their favourite planet.

In their wisdom, the IAU came up with a new class of heavenly body, "dwarf planet", which would include Pluto. Dwarf planets, incidentally, are not planets that are dwarfy. They are something completely different, the IAU said.

It's all wonderful, if deeply baffling stuff. Why is this happening? Whatever your views on Pluto's rightful status, it's heartening to see that the fate of that small rock, and so the size of the solar system, is still up in the air.